Even though there is a good chance for the frame to be Liberia made, I don't want to come off as disrespectful or anything and I'm still searching for other producers. Somebody suggested this frame may be a France-Loire.

On this note, I removed the BB cable guide (looks made from aluminium) and discovered there is a star shape stamp. Does this mean something?
Don't know if there are some other stamps under the paint. I decided to treat and remove the old paint and then, I'll inspect the frame more carefully, searching for clues.